The invention relates to telecommunications systems and, more particularly, to the characterization of subscriber loops, that is, of the connection between a telephone office and subscriber premises.
In eighteen seventy-six, inside a third floor walk-up garret apartment in the Scollay Square section of Boston Massachusetts, only a short distance from the sight of the first battle of the revolutionary war, Alexander Graham Bell spoke the first words transmitted over telephone wires. Bell""s transmission of sound over telephone wires initiated a revolution in communications whose scope rivals that of the political revolution initiated by the sound, heard nearby, of xe2x80x9cthe shot heard round the world.xe2x80x9d
Technical innovations have dramatically transformed the telecommunications industry in the ensuing years. For example, telecommunications switching systems have evolved considerably from xe2x80x9chand operatedxe2x80x9d systems in which one instrument was electrically connected (through a hierarchical switching network) to another with the intervention of a human operator who would physically plug one circuit into another. Such direct electrical connection of two or more channels between two points (at least one channel in each direction), a connection that provides a user with exclusive use of the channels to exchange information, is referred to as circuit switching, or line switching. Human operators have largely been replaced by systems which employ electronic switching systems (ESS, e.g., 5ESS), in which the instruments are automatically connected through the network by electronic systems. Nevertheless, such switching systems often still employ circuit switching, a technique which yields highly reliable service, particularly for such xe2x80x9creal timexe2x80x9d communications applications as voice, in which the momentary loss of a channel is annoying, and repeated such losses are unacceptable.
Not only has switching technology undergone major changes, the type of traffic being carried on telephone lines has also changed dramatically. Although originally designed for voice traffic and xe2x80x9ctunedxe2x80x9d to operation in the voice band between approximately 350 and 4000 Hz, the telecommunications infrastructure also carries data, through the use of various channels, or signals, such as tones. However, with the growing use of the Internet, and the potential development such high bandwidth applications such as interactive distance-learning and video on demand, the existing telecommunications infrastructure is in danger of being overwhelmed. A large portion of the system""s transmission medium has been replaced with high speed trunks which employ fiber optic transmission media, microwave media, and line of sight optical media, for example, to meet the ever mounting demand for high speed data transmission capability. However, a huge installed base of transmission media, composed primarily of twisted pair copper wire, forms the telecommunications path from service providers"" central offices to customer premises. Designed for low-frequency voice grade operation, this xe2x80x9clast milexe2x80x9d of connectivity presents a bottleneck to high-speed operations.
Nevertheless, technologies, such as digital subscriber line (DSL) provide relatively high-speed data transmission over this somewhat archaic installed base of copper local loops. To provide such high speed data services over copper lines, a provider, such as a local telephone operating company, may estimate the transmission capacity of all the local loops that terminate within a given central office, and offer a xe2x80x9cblanketxe2x80x9d service for all those loops. For example, a local telephone service provider may estimate or otherwise determine that 1.54 Mbps DSL service may be provided to a number of customers whose local loops are terminated a given central office. Typically, the local telephone service provider will not know the data-transmission capacity of each of the loops thus terminated and, by using an estimate with a margin of safety, will waste a significant amount of unused capacity. That is, many of the loops terminated at the central office may be capable of providing significantly higher data rate operations but, because the local service provider has no idea which loops, if any, are capable of supporting higher speed transmissions, the service provider guarantees operations at a much lower data rate than might be supported by some number of loops associated with the central office. Additionally, even with a margin of error built in to the service offerings, some of the loops may not be capable of handling the guaranteed data rate and, as a result, costly reconfigurations may be required to upgrade a customer""s service to the guaranteed level. A system for accurately characterizing the data transmission capacity of local loops would therefore be highly desirable.
A system in accordance with the principles of the present invention employs a loop field test to determine the characteristics of a reference loop. This characterization is then used to predict the data transmission capability of at least one similar loop. In accordance with the principles of the invention, a local loop may be selected for testing and have field tests performed on it. The loop may be characterized, based on the results of the field test, and the data rate capability of other loops having similar characteristics may be predicted, based on the data rate capability of the field-tested loop. In an illustrative embodiment, the field test includes wideband noise testing of the selected loop. A transfer function of the field-tested loop is developed, based on the results of these tests. The similar loops whose data rate performances may be predicted on the basis of the reference loop characterization may be selected on the basis of geographic similarity, for example.
Thousands of local loops may be serviced by, or terminated in, a given central office. In accordance with the principles of the present invention, the local loops may be divided into a number of geographically diverse routes, each of which may be subject to differing environmental factors, such as electromagnetic interference. The differing environmental factors typically impose corresponding limits on the data transmission capability of the local loops. Each of the geographically diverse route cables may be further divided into carrier service area (CSA) groups, and the loops within a binder group may be cross connected at a binder post to provide service to a particular area. In an illustrative embodiment in which a central office serves 30,000 local loops, and is divided into six geographically diverse routes, the geographically diverse routes each includes ten binder posts, each binder post includes ten binder groups and each binder group includes fifty local loops. In this illustrative embodiment at least one local loop, referred to as a reference loop, within each binder group is field tested. The tested local loop, a reference loop, is characterized, at least in part, by the development of a transfer function. This characterization is used to predict the data rate capability of other local loops within the binder group.
In accordance with another aspect of the invention, one or more digital subscriber line modems may be qualified on the tested loop and, by extension, on similar loops. xe2x80x9cSimilar loopsxe2x80x9d may refer to loops within the same binder group.